sqlreview: structured-DDL rules from JSqlParser 5.4 (NOT NULL without default, CREATE INDEX without CONCURRENTLY, …)

[babltiga]

Context

JSqlParser 5.4 (#1077) now parses DDL into structured parts that 5.3 only kept as raw text:

• ALTER COLUMN nullability actions and default expressions
• column data types with precision / scale as properties
• PostgreSQL CREATE INDEX clauses (CONCURRENTLY, INCLUDE, partial WHERE, …)
• column defaults in CREATE TABLE

That lets the deterministic SQL review engine (#860, docs/19-sql-review.md) check migrations for dangerous shapes from the AST alone, which also benefits schema change set authoring (#870). There, a BLOCK refuses the save.

Proposal

Add built-in rules to sqlreview/internal/rules/SqlRuleCatalog, for example:

• add_not_null_column_without_default: ALTER TABLE … ADD COLUMN … NOT NULL with no DEFAULT fails, or rewrites the table, on a non-empty table.
• create_index_without_concurrently (PostgreSQL): a plain CREATE INDEX takes a lock that blocks writes to the table.
• column_type_narrowing: ALTER COLUMN … TYPE to a shorter length or lower precision / scale can truncate data or fail.
• set_not_null_on_existing_column: ALTER COLUMN … SET NOT NULL scans the whole table under an exclusive lock.

Pick the final set and the default severities during implementation.

Acceptance criteria

• Each rule is AST-only, follows the SqlRule contract, and has name / description / message keys in every messages file (MessagesParityTest).
• Dialect-specific rules report applicable:false (or skip) on engines where they don't apply.
• A unit test per rule, following the existing *RuleTest pattern (parse → evaluate → findings).
• The rules appear in the GET /sql-review/rules catalog and on the /admin/sql-review page with no frontend change beyond locale strings.
• docs/19-sql-review.md lists the new rules.

Depends on #1077 (JSqlParser 5.4).